A well-known portable phone having a packet communications function is capable of downloading content such as image data, music data, movie data, programs (e.g. Java™ application programs), and the like from a content provider in a network.
A new type of a portable phone has been developed recently, as disclosed in JP 2002-135407, such a phone being equipped with a data storage module (hereinafter referred to as a UIM (User Identity Module)), and subscriber information being stored in the UIM instead of in the memory of the phone itself. In a UIM, personal information of a user such as the user's credit card number, bank account number, telephone directory, and the like are stored in addition to the subscriber information. A user can remove a UIM from his/her own portable phone and insert the UIM into a portable phone owned by a third person, to thereby use the portable phone owned by the third person as if it were his/her own phone. Thus, a user is able to engage in voice and/or packet communication using a third person's portable phone by inserting his/her own UIM into the third person's phone, since information unique to each user (subscriber information and personal information described above) is stored in a UIM owned by respective users and transferred to any connected portable phone to effect voice and/or packet communication. In this case, communication charges incurred by voice and/or packet communication are billed to a user identified according to subscriber information stored in a UIM, not to the owner of a portable phone.
In a case that a user of a UIM downloads content from a content provider, access to the downloaded content is usually restricted to the user because s/he is the only person authorized by the content provider on the basis of satisfying certain conditions, for example, paying monthly charges for using application software. Ideally, a UIM would be used to store in addition to user ID and the like a substantial amount of downloaded content. However, the physical limitations of a UIM card prevent such storage, and it is feasible to store only a small amount of such information in a memory of the UIM. Thus, it is necessary to store most downloaded content in a memory storage space available in a portable phone into which a UIM is inserted.
However, a problem may arise in such a situation that if a user A inserts his/her own UIM into a user B's portable phone, and is able to use that phone without restriction, content downloaded by the user B can be accessed and read by the user A; or user A may write and store his/her downloaded content into user B's phone. Such usage of a third party's phone to access and/or store downloaded content may lead to a situation in which content originating at a content server, i.e., a content provider, and that is intended for and restricted to use by an authorized user is accessed and used by another, unauthorized, user.